Crystallization properties of polyhydroxybutyrate with modified silicas

The crystallization behaviors of polyhydroxybutyrate (PHB) filled with hydrophobic silica and hydrophilic silica that surface modified by methyl methacrylate (MMA) and amidoamine (AMDA) were analyzed by isothermal and dynamic differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide angle X-ray diffraction (WAXD). The results of DSC indicated that the presence of the hydrophobic silica or modified hydrophilic silica could notably increase the crystallization rate but decrease the crystallization activation energy and the melting-recrystallization degree of PHB. The decreases of spherulite sizes but increases of ordered crystallite sizes in PHB by the MMA and AMDA modified silicas were also confirmed by POM and WAXD. The modified hydrophilic silica, especially the AMDA modified, would have much better effects on enhancing crystallization speeds and forming better crystal structures than the unmodified hydrophilic silica due to the better compatibility with PHB. The significant effect of the silica surface on affecting the crystallization behavior and the subsequent melting behavior of PHB was confirmed.